Method and apparatus for three-dimensional fabrication

ABSTRACT

A method of making a three-dimensional object includes: (a) providing an apparatus comprising a radiation source, a carrier, and a movable belt positioned therebetween, with the belt comprised of an optically transparent material, and with the belt permeable to a polymerization inhibitor; (b) applying a polymerizable liquid to a first surface of the belt, and contacting a second surface of the belt to the polymerization inhibitor, (c) contacting a portion of the first surface to the carrier or the three dimensional object so that the belt adheres thereto with the polymerizable liquid positioned therebetween; (d) irradiating the polymerizable liquid with actinic radiation through the belt from the radiation source to polymerize the polymerizable liquid positioned therebetween; then (e) optionally separating the belt from the carrier or the three dimensional object; and then (f) repeating steps (b) through (e) until the three dimensional object is completed.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/255,752, filed Sep. 2, 2016, which claims the benefit of U.S.Provisional Patent Application Ser. No. 62/216,014, filed Sep. 9, 2015,the disclosures of which are incorporated by reference herein in theirentireties.

FIELD OF THE INVENTION

The present invention concerns methods and apparatus for the fabricationof three-dimensional objects, particularly larger objects, fromhardenable materials.

BACKGROUND OF THE INVENTION

Production of large objects such as automotive parts by additivemanufacturing techniques has been challenging.

Some approaches, such as “bottom up” three-dimensional fabrication,require resin to flow longer distances through the narrow space betweenthe growing object and the resin source during fabrication of largerobjects: A particular problem with viscous resins and solid objects.

Other approaches, such as “top down” three-dimensional fabrication,require larger objects to be lowered into larger baths or reservoirs ofthe resin during fabrication: A particular problem with resins that areexpensive, and/or have a relatively short “pot life.”

U.S. Pat. No. 5,247,180 to Mitcham describes a stereolithographyapparatus in which an object is lowered into a vat of polymerizableliquid, with the device employing a movable exposure head that travelsacross the surface of a growing object to allow fabrication of largerobjects. This, however, does not solve the problem of placing largeamounts of potentially expensive, and in some cases short pot-life,materials in a large vat or open space (see also L. Goreta, PCTApplication WO 1995/15841, and A. Allanic, PCT Application WO2014/108473). Accordingly, there is a need for new approaches toadditive manufacturing that are readily adaptable to the production oflarger objects.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a method of making athree-dimensional object, comprising:

(a) providing an apparatus comprising a radiation source, a carrier onwhich the three dimensional object is made, and a movable beltpositioned therebetween, the belt having a first surface and an oppositesecond surface, with the belt comprised of an optically transparentmaterial, and with the belt permeable to a polymerization inhibitor;

(b) applying a polymerizable liquid to the first surface of the belt,and contacting the second surface of the belt to the polymerizationinhibitor,

(c) contacting a portion of the belt first surface having thepolymerizable liquid thereon to the carrier or the three dimensionalobject so that the belt adheres thereto with the polymerizable liquidpositioned therebetween;

(d) irradiating the polymerizable liquid with actinic radiation throughthe belt from the radiation source to polymerize the polymerizableliquid positioned therebetween, and/or while:

-   -   (i) moving the radiation source lengthwise across the substrate        or the three-dimensional object (e.g., while the belt is in        static contact with the carrier or object; that is, does not        slide);    -   (ii) continuously adhering a leading edge portion of the belt to        the carrier or the object;    -   (iii) continuously peeling a trailing edge portion of the belt        from the carrier or the object, with    -   (iv) the polymerization inhibitor passing through the belt to        form an active surface on the object (e.g., which active surface        persists after separating step (e) and new contact (c) is made,        to facilitate continuous covalent coupling of newly deposited        material to previously deposited material), and optionally, a        dead zone of unpolymerized liquid between the active surface and        the polymerizable liquid; then

(e) optionally separating the belt from the carrier or the threedimensional object (e.g., to begin re-applying the polymerizable liquidto the belt); and then

(f) repeating steps (b) through (e) until the three dimensional objectis completed.

A further aspect of the invention is an apparatus useful for making athree-dimensional object, comprising:

(a) a radiation source,

(b) a carrier on which the three dimensional object is made;

(c) a movable belt positioned between the carrier and the radiationsource, the belt having a first surface and an opposite second surface,with the belt comprised of an optically transparent material, and withthe belt permeable to a polymerization inhibitor;

(d) an applicator assembly operably associated with the belt andconfigured to apply a polymerizable liquid thereto;

(e) a frame, with the belt and the radiation source connected to theframe, and with the frame defining a contact region in which the beltcontacts the carrier or object;

(f) a first drive assembly interconnecting the movable belt and theframe;

(g) a second drive assembly interconnecting the frame and the carrier.

In some embodiments, the radiation source, movable belt, applicatorassembly, first drive assembly, and frame are provided separately fromthe carrier and the second drive assembly, as a “head assembly” whichmay be mounted to a carrier and associated drives (e.g., mounted orretrofitted to a CNC machine).

Non-limiting examples and specific embodiments of the present inventionare explained in greater detail in the drawings herein and thespecification set forth below. The disclosure of all United StatesPatent references cited herein are to be incorporated herein byreference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Schematic illustration of method and apparatus.

FIG. 2: Perspective view of one embodiment of apparatus.

FIG. 3: CAD model (left) and parts produced (right).

FIG. 4: Single-Pass (left) and Multi-Pass (right) deposition patterns.

FIG. 5: Alternate embodiment of method and apparatus.

FIG. 6: Embodiment of FIG. 5 operating in reverse direction.

FIG. 7: Schematic illustration of offset curing zones in successivedeposition passes.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is now described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein; rather these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe scope of the invention to those skilled in the art.

Like numbers refer to like elements throughout. In the figures, thethickness of certain lines, layers, components, elements or features maybe exaggerated for clarity. Where used, broken lines illustrate optionalfeatures or operations unless specified otherwise.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises” or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements components and/orgroups or combinations thereof, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components and/or groups or combinations thereof.

As used herein, the term “and/or” includes any and all possiblecombinations or one or more of the associated listed items, as well asthe lack of combinations when interpreted in the alternative (“or”).

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the specification andclaims and should not be interpreted in an idealized or overly formalsense unless expressly so defined herein. Well-known functions orconstructions may not be described in detail for brevity and/or clarity.

It will be understood that when an element is referred to as being “on,”“attached” to, “connected” to, “coupled” with, “contacting,” etc.,another element, it can be directly on, attached to, connected to,coupled with and/or contacting the other element or intervening elementscan also be present. In contrast, when an element is referred to asbeing, for example, “directly on,” “directly attached” to, “directlyconnected” to, “directly coupled” with or “directly contacting” anotherelement, there are no intervening elements present. It will also beappreciated by those of skill in the art that references to a structureor feature that is disposed “adjacent” another feature can have portionsthat overlap or underlie the adjacent feature.

Spatially relative terms, such as “under,” “below,” “lower,” “over,”“upper” and the like, may be used herein for ease of description todescribe an element's or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is inverted, elements described as “under” or “beneath” otherelements or features would then be oriented “over” the other elements orfeatures. Thus the exemplary term “under” can encompass both anorientation of over and under. The device may otherwise be oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly. Similarly, the terms“upwardly,” “downwardly,” “vertical,” “horizontal” and the like are usedherein for the purpose of explanation only, unless specificallyindicated otherwise.

It will be understood that, although the terms first, second, etc., maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. Rather, these terms areonly used to distinguish one element, component, region, layer and/orsection, from another element, component, region, layer and/or section.Thus, a first element, component, region, layer or section discussedherein could be termed a second element, component, region, layer orsection without departing from the teachings of the present invention.The sequence of operations (or steps) is not limited to the orderpresented in the claims or figures unless specifically indicatedotherwise.

1. Polymerizable Liquids

Any suitable polymerizable liquid that includes a component that iscured by actinic radiation or light, particularly UV light, may be usedto carry out the present invention. In some embodiments, thepolymerizable liquid may be a “dual cure” polymerizable liquid thatadditionally includes components that are cured by a different mechanism(heat, microwave irradiation, light at a different wavelength, etc.).Where a second cure is employed after a “green” part is initiallyfabricated, in some embodiments reaction products of the first cure mayserve as reactants, or precursors, for the second cure.

In some embodiments, the polymerizable liquid has a limited “pot life:”That is, constituents begin to react within one or two hours, underconditions in which the polymerizable liquid is used.

In some embodiments, the polymerizable liquid has a high viscosity: Forexample, a viscosity of 1,000 or 2,000 centipoise or more, or even aviscosity of 10,000 or 20,000 centipoise or more, under conditions inwhich the method is carried out.

Examples of suitable polymerizable liquids include, but are not limitedto, those described in US Patent Application Publication No.2015/0102532 to DeSimone et al.

In general, when the polymerizable liquid comprises a free radicalpolymerizable liquid, the inhibitor may oxygen (e.g., atmosphericoxygen). When the first polymerizable liquid comprises an acid-catalyzedor cationically polymerizable liquid, and the inhibitor may comprise abase.

Additional examples of polymerizable liquids that may be used to carryout the present invention include, but are not limited to, the dual curepolymerizable liquids discussed further below.

2. Apparatus

As noted above, an apparatus useful for making a three-dimensionalobject, as described herein may comprise (see, e.g., FIGS. 1-2 and 5-6):

(a) a radiation source, typically an actinic radiation source (e.g., alight source, such as an ultraviolet light source 11);

(b) a carrier or “build platform” 15 on which the three dimensionalobject is made;

(c) a movable belt or film 13 positioned between the carrier and theradiation source, the belt having a first surface and an opposite secondsurface, with the belt comprised of an optically transparent material,and with the belt permeable to a polymerization inhibitor (e.g.atmospheric oxygen);

(d) an applicator assembly operably associated with the belt andconfigured to apply a polymerizable liquid thereto;

(e) a frame 16, with the belt and the radiation source connected to theframe, and with the frame defining a contact region in which the beltcontacts the carrier or object;

(f) a first drive assembly interconnecting the movable belt and theframe; and

(g) a second drive assembly interconnecting the frame and the carrier.

The moving belt may be continuous or discontinuous (that is, reversiblein direction, being alternately taken up and unwound from a spool orroller). The moving belt is generally formed of a material that isflexible, optically transparent or transparent to the actinic radiation(e.g., ultraviolet light), and permeable to the inhibitor ofpolymerization (e.g., atmospheric oxygen). In some embodiments, the beltis formed of a fluoropolymer.

In general, the moving belt is configured (e.g., by mounting on rollers12 or the like) to pass through a contact region (e.g., defined by aleading edge portion and a trailing peeling edge portion) which contactregion is in fixed contact (e.g., non-slipping contact) with the carrieror the object. Note that the contact region has a length dimension lessthan that of the carrier or the object.

Any suitable applicator assembly may be used, including but not limitedto rollers, sprayers 22, blades, baths, and combinations thereof. Insome embodiments the applicator assembly comprises a plurality ofindependently controllable spray orifices, such as an ink-jet spray heador cartridge.

Control systems and associated wiring are not shown in the Figures forclarity, but may be implemented in accordance with known techniques.

3. Methods

A method of making a three-dimensional object may be carried out withapparatus such as described above by:

(a) providing an apparatus comprising a radiation source, a carrier onwhich the three dimensional object is made, and a movable beltpositioned therebetween, the belt having a first surface and an oppositesecond surface, with the belt comprised of an optically transparentmaterial, and with the belt permeable to a polymerization inhibitor(e.g., atmospheric oxygen);

(b) applying a polymerizable liquid to the first surface of the belt,and contacting the second surface of the belt to the polymerizationinhibitor,

(c) contacting a portion of the belt first surface having thepolymerizable liquid thereon to the carrier or the three dimensionalobject so that the belt adheres thereto with the polymerizable liquidpositioned therebetween;

(d) irradiating the polymerizable liquid with actinic radiation throughthe belt from the radiation source to polymerize the polymerizableliquid positioned therebetween, and or while:

-   -   (i) moving the radiation source lengthwise across the substrate        or the three-dimensional object (e.g., while the belt is in        static contact with the carrier or object; that is, does not        slide);    -   (ii) continuously adhering a leading edge portion of the belt to        the carrier or the object;    -   (iii) continuously peeling a trailing edge portion of the belt        from the carrier or the object, with    -   (iv) the polymerization inhibitor passing through the belt to        form an active surface on the object (e.g., which active surface        persists after separating step (e) and new contact (c) is made,        to facilitate continuous covalent coupling of newly deposited        material to previously deposited material), and optionally, a        dead zone of unpolymerized liquid between the active surface and        the polymerizable liquid; then

(e) optionally separating the belt from the carrier or the threedimensional object (e.g., to begin re-applying the polymerizable liquidto the belt); and then

(f) repeating steps (b) through (e) until the three dimensional objectis completed.

The irradiating step may be carried out with patterned actinicradiation, to produce the three dimensional object in accordance withknown techniques. However, in some embodiments, the irradiating maysimply be “flood” irradiation, and the configuration of the threedimensional object achieved by patterned coating of the belt with thepolymerizable liquid (e.g., by patterned spray from a plurality of sprayorifices, such as patterned spray application with an ink-jet sprayassembly). In still other embodiments, both patterned actinic radiation,and patterned coating of the belt, may be employed in combination withone another.

The separating step (e) may be carried out by (i) advancing the beltcontact region lengthwise beyond the carrier or the three dimensionalobject, and then (ii) advancing the belt contact region and the carrieror the three dimensional object in the height dimension.

In some embodiments, the repeating step (f) may be carried out byrepeatedly reversing the direction of travel of the belt and radiationsource. In this case, complete separation may not be required, as atrailing edge (to then become the leading edge after reversal ofdirection) may remain in contact with the object. This embodiment may bedesirable where the belt is not “endless” or continuous, but is taken upand unwound from various spools or reels. In other embodiments (whichmay be employed when the belt is continuous), the repeating step may becarried out by (f) is carried out by (i) lifting or spacing the beltabove the three dimensional object; (ii) moving the belt and radiationsource lengthwise across the three dimensional object without contactingthe same to return the belt and radiation source to a start position;and (iii) repeating steps (b) through (e) in the same direction oftravel as in the previous repetition of steps (b) through (e) In eithercase, the repeating step may include laterally shifting the belt andradiation source with respect to the direction of travel prior torepeating steps (b) through (e), to obtain exposure of larger surfaceareas on the object by a belt having a lesser width.

In some embodiments, the belt is electrostatically charged, and/or theapplying step is carried out by electrospray.

In some embodiments, the belt may be pressed against the carrier or theobject (e.g., with an optically transparent pressure plate positionedbetween the belt and carrier or three dimensional object) to promoteuniform coating of the object with the polymerizable liquid.

While the carrier and belt may be repeatedly re-positioned with respectto one another during the fabrication of the three-dimensional object,it may be desirable in some embodiments to co-fabricate a sacrificialleading bumper and/or sacrificial trailing bumper on the carrier, alongwith the object (for example, where tolerances are close andre-alignment of the belt with the growing object may be required). Suchbumpers may be in any suitable shape, such as in the shape of a ramp.The bumpers may be fabricated of the same material as the object, or,through the use of multiple selectable spray orifices or the likeapplying different polymerizable liquids to different regions of thebelt, be fabricated from different materials as the object. The bumpersmay be “over exposed” during fabrication so that they are harder thanthe object itself, and/or layered.

4A. Dual Cure Polymerizable Liquids: Part A

Dual cure systems as described herein may include a first curable system(sometimes referred to as “Part A” or herein) that is curable by actinicradiation, typically light, and in some embodiments ultraviolet (UV)light). Any suitable polymerizable liquid can be used as the firstcomponent. The liquid (sometimes also referred to as “liquid resin”“ink,” or simply “resin” herein) can include a monomer, particularlyphotopolymerizable and/or free radical polymerizable monomers, and asuitable initiator such as a free radical initiator, and combinationsthereof. Examples include, but are not limited to, acrylics,methacrylics, acrylamides, styrenics, olefins, halogenated olefins,cyclic alkenes, maleic anhydride, alkenes, alkynes, carbon monoxide,functionalized oligomers, multifunctional cure site monomers,functionalized PEGs, etc., including combinations thereof. Examples ofliquid resins, monomers and initiators include but are not limited tothose set forth in U.S. Pat. Nos. 8,232,043; 8,119,214; 7,935,476;7,767,728; 7,649,029; WO 2012129968 A1; CN 102715751 A; JP 2012210408 A.

Acid catalyzed polymerizable liquids. While in some embodiments as notedabove the polymerizable liquid comprises a free radical polymerizableliquid (in which case an inhibitor may be oxygen as described below), inother embodiments the polymerizable liquid comprises an acid catalyzed,or cationically polymerized, polymerizable liquid. In such embodimentsthe polymerizable liquid comprises monomers contain groups suitable foracid catalysis, such as epoxide groups, vinyl ether groups, etc. Thussuitable monomers include olefins such as methoxyethene,4-methoxystyrene, styrene, 2-methylprop-1-ene, 1,3-butadiene, etc.;heterocycloic monomers (including lactones, lactams, and cyclic amines)such as oxirane, thietane, tetrahydrofuran, oxazoline, 1,3, dioxepane,oxetan-2-one, etc., and combinations thereof. A suitable (generallyionic or non-ionic) photoacid generator (PAG) is included in the acidcatalyzed polymerizable liquid, examples of which include, but are notlimited to onium salts, sulfonium and iodonium salts, etc., such asdiphenyl iodide hexafluorophosphate, diphenyl iodide hexafluoroarsenate,diphenyl iodide hexafluoroantimonate, diphenyl p-methoxyphenyl triflate,diphenyl p-toluenyl triflate, diphenyl p-isobutylphenyl triflate,diphenyl p-tert-butylphenyl triflate, triphenylsulfoniumhexafluororphosphate, triphenylsulfonium hexafluoroarsenate,triphenylsulfonium hexafluoroantimonate, triphenylsulfonium triflate,dibutylnaphthylsulfonium triflate, etc., including mixtures thereof.See, e.g., U.S. Pat. Nos. 7,824,839; 7,550,246; 7,534,844; 6,692,891;5,374,500; and 5,017,461; see also Photoacid Generator Selection Guidefor the electronics industry and energy curable coatings (BASF 2010).

Hydrogels. In some embodiments suitable resins includes photocurablehydrogels like poly(ethylene glycols) (PEG) and gelatins. PEG hydrogelshave been used to deliver a variety of biologicals, including Growthfactors; however, a great challenge facing PEG hydrogels crosslinked bychain growth polymerizations is the potential for irreversible proteindamage. Conditions to maximize release of the biologicals fromphotopolymerized PEG diacrylate hydrogels can be enhanced by inclusionof affinity binding peptide sequences in the monomer resin solutions,prior to photopolymerization allowing sustained delivery. Gelatin is abiopolymer frequently used in food, cosmetic, pharmaceutical andphotographic industries. It is obtained by thermal denaturation orchemical and physical degradation of collagen. There are three kinds ofgelatin, including those found in animals, fish and humans. Gelatin fromthe skin of cold water fish is considered safe to use in pharmaceuticalapplications. UV or visible light can be used to crosslink appropriatelymodified gelatin. Methods for crosslinking gelatin include curederivatives from dyes such as Rose Bengal.

Photocurable silicone resins. A suitable resin includes photocurablesilicones. UV cure silicone rubber, such as Siliopren™ UV Cure SiliconeRubber can be used as can LOCTITE™ Cure Silicone adhesives sealants.Applications include optical instruments, medical and surgicalequipment, exterior lighting and enclosures, electricalconnectors/sensors, fiber optics and gaskets.

Biodegradable resins. Biodegradable resins are particularly importantfor implantable devices to deliver drugs or for temporary performanceapplications, like biodegradable screws and stents (U.S. Pat. Nos.7,919,162; 6,932,930). Biodegradable copolymers of lactic acid andglycolic acid (PLGA) can be dissolved in PEG dimethacrylate to yield atransparent resin suitable for use. Polycaprolactone and PLGA oligomerscan be functionalized with acrylic or methacrylic groups to allow themto be effective resins for use.

Photocurable polyurethanes. A particularly useful resin is photocurablepolyurethanes (including, polyureas, and copolymers of polyurethanes andpolyureas (e.g., poly(urethane-urea)). A photopolymerizablepolyurethane/polyurea composition comprising (1) a polyurethane based onan aliphatic diisocyanate, poly(hexamethylene isophthalate glycol) and,optionally, 1,4-butanediol; (2) a polyfunctional acrylic ester; (3) aphotoinitiator; and (4) an anti-oxidant, can be formulated so that itprovides a hard, abrasion-resistant, and stain-resistant material (U.S.Pat. No. 4,337,130). Photocurable thermoplastic polyurethane elastomersincorporate photoreactive diacetylene diols as chain extenders.

Additionally photocurable urethane acrylate resins are particularlyuseful. These resins comprise an oligomeric diol, for example, poly(tetramethylene oxide) diol, that is first end-capped with adiisocyanate, for example isophorone diisocyanate. This resultingprepolymer is made photocurable by subsequent reaction with a monomercontaining both a vinyl functionality and a second functional group thatwill react with an isocyanate. For example, 2-hydroxy ethyl acrylate canbe added to the prepolymer to yield a photocurable urethane acrylate. Avariety of materials can be made by varying the diol composition andmolecular weight, the isocyanate composition and ratio to the diol, andthe composition of the reactive monomer. Optionally, these urethaneacrylates can be blended with a reactive diluent, isobornyl acrylate,for example, to lower viscosity and further adjust properties.

High performance resins. In some embodiments, high performance resinsare used. Such high performance resins may sometimes require the use ofheating to melt and/or reduce the viscosity thereof, as noted above anddiscussed further below. Examples of such resins include, but are notlimited to, resins for those materials sometimes referred to as liquidcrystalline polymers of esters, ester-imide, and ester-amide oligomers,as described in U.S. Pat. Nos. 7,507,784; 6,939,940. Since such resinsare sometimes employed as high-temperature thermoset resins, in thepresent invention they further comprise a suitable photoinitiator suchas benzophenone, anthraquinone, and fluoroenone initiators (includingderivatives thereof), to initiate cross-linking on irradiation, asdiscussed further below.

Additional example resins. Particularly useful resins for dentalapplications include EnvisionTEC's Clear Guide, EnvisionTEC's E-DenstoneMaterial. Particularly useful resins for hearing aid industries includeEnvisionTEC's e-Shell 300 Series of resins. Particularly useful resinsinclude EnvisionTEC's HTM140IV High Temperature Mold Material for usedirectly with vulcanized rubber in molding/casting applications. Aparticularly useful material for making tough and stiff parts includesEnvisionTEC's RC31 resin. Particularly useful resin for investmentcasting applications include EnvisionTEC's Easy Cast EC500 resin andMadeSolid FireCast resin.

Additional resin ingredients. The liquid resin or polymerizable materialcan have solid particles suspended or dispersed therein. Any suitablesolid particle can be used, depending upon the end product beingfabricated. The particles can be metallic, organic/polymeric, inorganic,or composites or mixtures thereof. The particles can be nonconductive,semi-conductive, or conductive (including metallic and non-metallic orpolymer conductors); and the particles can be magnetic, ferromagnetic,paramagnetic, or nonmagnetic. The particles can be of any suitableshape, including spherical, elliptical, cylindrical, etc. The particlescan be of any suitable size (for example, ranging from 1 nm to 20 umaverage diameter).

The particles can comprise an active agent or detectable compound asdescribed below, though these may also be provided dissolved solubilizedin the liquid resin as also discussed below. For example, magnetic orparamagnetic particles or nanoparticles can be employed.

The liquid resin can have additional ingredients solubilized therein,including pigments, dyes, active compounds or pharmaceutical compounds,detectable compounds (e.g., fluorescent, phosphorescent, radioactive),etc., again depending upon the particular purpose of the product beingfabricated. Examples of such additional ingredients include, but are notlimited to, proteins, peptides, nucleic acids (DNA, RNA) such as siRNA,sugars, small organic compounds (drugs and drug-like compounds), etc.,including combinations thereof.

Non-reactive light absorbers. In some embodiments, polymerizable liquidsfor carrying out the present invention include a non-reactive pigment ordye that absorbs light, particularly UV light. Suitable examples of suchlight absorbers include, but are not limited to: (i) titanium dioxide(e.g., included in an amount of from 0.05 or 0.1 to 1 or 5 percent byweight), (ii) carbon black (e.g., included in an amount of from 0.05 or0.1 to 1 or 5 percent by weight), and/or (iii) an organic ultravioletlight absorber such as a hydroxybenzophenone,hydroxyphenylbenzotriazole, oxanilide, benzophenone,hydroxypenyltriazine, and/or benzotriazole ultraviolet light absorber(e.g., Mayzo BLS1326) (e.g., included in an amount of 0.001 or 0.005 to1, 2 or 4 percent by weight). Examples of suitable organic ultravioletlight absorbers include, but are not limited to, those described in U.S.Pat. Nos. 3,213,058; 6,916,867; 7,157,586; and 7,695,643, thedisclosures of which are incorporated herein by reference.

Inhibitors of polymerization. Inhibitors or polymerization inhibitorsfor use in the present invention may be in the form of a liquid or agas. In some embodiments, gas inhibitors are preferred. The specificinhibitor will depend upon the monomer being polymerized and thepolymerization reaction. For free radical polymerization monomers, theinhibitor can conveniently be oxygen, which can be provided in the formof a gas such as air, a gas enriched in oxygen (optionally but in someembodiments preferably containing additional inert gases to reducecombustibility thereof), or in some embodiments pure oxygen gas. Inalternate embodiments, such as where the monomer is polymerized byphotoacid generator initiator, the inhibitor can be a base such asammonia, trace amines (e.g. methyl amine, ethyl amine, di and trialkylamines such as dimethyl amine, diethyl amine, trimethyl amine, triethylamine, etc.), or carbon dioxide, including mixtures or combinationsthereof.

Polymerizable liquids carrying live cells. In some embodiments, thepolymerizable liquid may carry live cells as “particles” therein. Suchpolymerizable liquids are generally aqueous, and may be oxygenated, andmay be considered as “emulsions” where the live cells are the discretephase. Suitable live cells may be plant cells (e.g., monocot, dicot),animal cells (e.g., mammalian, avian, amphibian, reptile cells),microbial cells (e.g., prokaryote, eukaryote, protozoal, etc.), etc. Thecells may be of differentiated cells from or corresponding to any typeof tissue (e.g., blood, cartilage, bone, muscle, endocrine gland,exocrine gland, epithelial, endothelial, etc.), or may beundifferentiated cells such as stem cells or progenitor cells. In suchembodiments the polymerizable liquid can be one that forms a hydrogel,including but not limited to those described in U.S. Pat. Nos.7,651,683; 7,651,682; 7,556,490; 6,602,975; 5,836,313; etc.

In some embodiments, polymerizable liquids used in the present inventioninclude a non-reactive pigment or dye. Examples include, but are notlimited to, (i) titanium dioxide (e.g., in an amount of from 0.05 or 0.1to 1 or 5 percent by weight), (ii) carbon black (e.g., included in anamount of from 0.05 or 0.1 to 1 or 5 percent by weight), and/or (iii) anorganic ultraviolet light absorber such as a hydroxybenzophenone,hydroxyphenylbenzotriazole, oxanilide, benzophenone,hydroxypenyltriazine, and/or benzotriazole ultraviolet light absorber(e.g. in an amount of 0.001 or 0.005 to 1, 2 or 4 percent by weight).

4B. Dual Cure Polymerizable Liquids: Part B

As noted above, in some embodiments of the invention, the polymerizableliquid comprises a first light polymerizable component (sometimesreferred to as “Part A” herein) and a second component that solidifiesby another mechanism, or in a different manner from, the first component(sometimes referred to as “Part B” herein), typically by furtherreacting, polymerizing, or chain extending. Numerous embodiments thereofmay be carried out. In the following, note that, where particularacrylates such as methacrylates are described, other acrylates may alsobe used.

Part A chemistry. As noted above, in some embodiments of the presentinvention, a resin will have a first component, termed “Part A.” Part Acomprises or consists of a mix of monomers and/or prepolymers that canbe polymerized by exposure to actinic radiation or light. This resin canhave a functionality of 2 or higher (though a resin with a functionalityof 1 can also be used when the polymer does not dissolve in itsmonomer). A purpose of Part A is to “lock” the shape of the object beingformed or create a scaffold for the one or more additional components(e.g., Part B). Importantly, Part A is present at or above the minimumquantity needed to maintain the shape of the object being formed afterthe initial solidification. In some embodiments, this amount correspondsto less than ten, twenty, or thirty percent by weight of the total resin(polymerizable liquid) composition.

In some embodiments, Part A can react to form a cross-linked polymernetwork or a solid homopolymer.

Examples of suitable reactive end groups suitable for Part Aconstituents, monomers, or prepolymers include, but are not limited to:acrylates, methacrylates, α-olefins, N-vinyls, acrylamides,methacrylamides, styrenics, epoxides, thiols, 1,3-dienes, vinyl halides,acrylonitriles, vinyl esters, maleimides, and vinyl ethers.

An aspect of the solidification of Part A is that it provides a scaffoldin which a second reactive resin component, termed “Part B,” cansolidify during a second step (which may occur concurrently with orfollowing the solidification of Part A). This secondary reactionpreferably occurs without significantly distorting the original shapedefined during the solidification of Part A. Alternative approacheswould lead to a distortion in the original shape in a desired manner.

In particular embodiments, when used in the methods and apparatusdescribed herein, the solidification of Part A is continuously inhibitedduring printing within a certain region, by oxygen or amines or otherreactive species, to form a liquid interface between the solidified partand an inhibitor-permeable film or window (e.g., is carried out bycontinuous liquid interphase/interface printing).

Part B chemistry. Part B may comprise, consist of or consist essentiallyof a mix of monomers and/or prepolymers that possess reactive end groupsthat participate in a second solidification reaction after the Part Asolidification reaction. In some embodiments, Part B could be addedsimultaneously to Part A so it is present during the exposure toactinide radiation, or Part B could be infused into the object madeduring the 3D printing process in a subsequent step. Examples of methodsused to solidify Part B include, but are not limited to, contacting theobject or scaffold to heat, water or water vapor, light at a differentwavelength than that at which Part A is cured, catalysts, (with orwithout additional heat), evaporation of a solvent from thepolymerizable liquid (e.g., using heat, vacuum, or a combinationthereof), microwave irradiation, etc., including combinations thereof.

Examples of suitable reactive end group pairs suitable for Part Bconstituents, monomers or prepolymers include, but are not limited to:epoxy/amine, epoxy/hydroxyl, oxetane/amine, oxetane/alcohol,isocyanate*/hydroxyl, Isocyanate*/amine, isocyanate/carboxylic acid,anhydride/amine, amine/carboxylic acid, amine/ester, hydroxyl/carboxylicacid, hydroxyl/acid chloride, amine/acid chloride, vinyl/Si—H(hydrosilylation), Si—Cl/hydroxyl, Si—Cl/amine, hydroxyl/aldehyde,amine/aldehyde, hydroxymethyl or alkoxymethyl amide/alcohol, aminoplast,alkyne/Azide (also known as one embodiment of “Click Chemistry,” alongwith additional reactions including thiolene, Michael additions,Diels-Alder reactions, nucleophilic substitution reactions, etc.),alkene/Sulfur (polybutadiene vulcanization), alkene/thiol, alkyne/thiol,hydroxyl/halide, isocyanate*/water (polyurethane foams), Si—OH/hydroxyl,Si—OH/water, Si—OH/Si—H (tin catalyzed silicone), Si—OH/Si—OH (tincatalyzed silicone), Perfluorovinyl (coupling to formperfluorocyclobutane), etc., where *Isocyanates include protectedisocyanates (e.g. oximes)), diene/dienophiles for Diels-Alder reactions,olefin metathesis polymerization, olefin polymerization usingZiegler-Natta catalysis, ring-opening polymerization (includingring-opening olefin metathesis polymerization, lactams, lactones,Siloxanes, epoxides, cyclic ethers, imines, cyclic acetals, etc.), etc.

Other reactive chemistries suitable for Part B will be recognizable bythose skilled in the art. Part B components useful for the formation ofpolymers described in “Concise Polymeric Materials Encyclopedia” and the“Encyclopedia of Polymer Science and Technology” are hereby incorporatedby reference.

Elastomers. A particularly useful embodiment for implementing theinvention is for the formation of elastomers. Tough, high-elongationelastomers are difficult to achieve using only liquid UV-curableprecursors. However, there exist many thermally cured materials(polyurethanes, silicones, natural rubber) that result in tough,high-elongation elastomers after curing. These thermally curableelastomers on their own are generally incompatible with most 3D printingtechniques.

In embodiments of the current invention, small amounts (e.g., less than20 percent by weight) of a low-viscosity UV curable material (Part A)are blended with thermally-curable precursors to form (preferably tough)elastomers (e.g. polyurethanes, polyureas, or copolymers thereof (e.g.,poly(urethane-urea)), and silicones) (Part B). The UV curable componentis used to solidify an object into the desired shape using 3D printingas described herein and a scaffold for the elastomer precursors in thepolymerizable liquid. The object can then be heated after printing,thereby activating the second component, resulting in an objectcomprising the elastomer.

Adhesion of formed objects. In some embodiments, it may be useful todefine the shapes of multiple objects using the solidification of PartA, align those objects in a particular configuration, such that there isa hermetic seal between the objects, then activate the secondarysolidification of Part B. In this manner, strong adhesion between partscan be achieved during production. A particularly useful example may bein the formation and adhesion of sneaker components.

Fusion of particles as Part B. In some embodiments, “Part B” may simplyconsist of small particles of a pre-formed polymer. After thesolidification of Part A, the object may be heated above the glasstransition temperature of Part B in order to fuse the entrappedpolymeric particles.

Evaporation of solvent as Part B. In some embodiments, “Part B” mayconsist of a pre-formed polymer dissolved in a solvent. After thesolidification of Part A into the desired object, the object issubjected to a process (e.g. heat+vacuum) that allows for evaporation ofthe solvent for Part B, thereby solidifying Part B.

Thermally cleavable end groups. In some embodiments, the reactivechemistries in Part A can be thermally cleaved to generate a newreactive species after the solidification of Part A. The newly formedreactive species can further react with Part B in a secondarysolidification. An exemplary system is described by Velankar, Pezos andCooper, Journal of Applied Polymer Science, 62, 1361-1376 (1996). Here,after UV-curing, the acrylate/methacrylate groups in the formed objectare thermally cleaved to generated diisocyanate prepolymers that furtherreact with blended chain-extender to give high molecular weightpolyurethanes/polyureas within the original cured material or scaffold.Such systems are, in general, dual-hardening systems that employ blockedor reactive blocked prepolymers, as discussed in greater detail below.It may be noted that later work indicates that the thermal cleavageabove is actually a displacement reaction of the chain extender (usuallya diamine) with the hindered urea, giving the finalpolyurethanes/polyureas without generating isocyanate intermediates.

Methods of mixing components. In some embodiments, the components may bemixed in a continuous manner prior to being introduced to the printerbuild plate. This may be done using multi-barrel syringes and mixingnozzles. For example, Part A may comprise or consist of a UV-curabledi(meth)acrylate resin, Part B may comprise or consist of a diisocyanateprepolymer and a polyol mixture. The polyol can be blended together inone barrel with Part A and remain unreacted. A second syringe barrelwould contain the diisocyanate of Part B. In this manner, the materialcan be stored without worry of “Part B” solidifying prematurely.Additionally, when the resin is introduced to the printer in thisfashion, a constant time is defined between mixing of all components andsolidification of Part A.

Other additive manufacturing techniques. It will be clear to thoseskilled in the art that the materials described in the current inventionwill be useful in other additive manufacturing techniques includingfused deposition modeling (FDM), solid laser sintering (SLS), andInk-jet methods. For example, a melt-processedacrylonitrile-butadiene-styrene resin may be formulated with a secondUV-curable component that can be activated after the object is formed byFDM. New mechanical properties could be achieved in this manner. Inanother alternative, melt-processed unvulcanized rubber is mixed with avulcanizing agent such as sulfur or peroxide, and the shape set throughFDM, then followed by a continuation of vulcanization.

5. Dual Cure Polymerizable Liquids Employing Blocked Constituents andThermally Cleavable Blocking Groups

In some embodiments, where the solidifying and/or curing step (d) iscarried out subsequent to the irradiating step (e.g., by heating ormicrowave irradiating); the solidifying and/or curing step (d) iscarried out under conditions in which the solid polymer scaffolddegrades and forms a constituent necessary for the polymerization of thesecond component (e.g., a constituent such as (i) a prepolymer, (ii) adiisocyanate or polyisocyanate, and/or (iii) a polyol and/or diol, wherethe second component comprises precursors to a polyurethane/polyurearesin). Such methods may involve the use of reactive or non-reactiveblocking groups on or coupled to a constituent of the first component,such that the constituent participates in the first hardening orsolidifying event, and when de-protected (yielding free constituent andfree blocking groups or blocking agents) generates a free constituentthat can participate in the second solidifying and/or curing event.Examples of such dual cure resins include, but are not limited to, thoseset forth in Jason P. Rolland et al., Three dimensional objects producedfrom materials having multiple mechanisms of hardening, US PatentApplication Pub. No. 2016016077 (9 Jun. 2016) (also published as PCTPatent Application Pub. No. WO2015/200189); Jason P. Rolland et al.,Methods of producing three dimensional objects from materials havingmultiple mechanisms of hardening US Patent Application Pub. No.20160136889 (19 May 2016) (also published as PCT Patent Application Pub.No. WO2015/200173); Jason P. Rolland et al., Methods of producingpolyurethane three-dimensional objects from materials having multiplemechanisms of hardening US Patent Application Pub. No. 20160137838 (19May 2016) (also published as PCT Patent Application Pub. No.WO2015/200179); and Jason P. Rolland et al., Polyurethane resins havingmultiple mechanisms of hardening for use in producing three-dimensionalobjects US Patent Application Pub. No. 20160137839 (19 May 2016) (alsopublished as PCT Patent Application Pub. No. WO2015/200201), thedisclosures of all of which are incorporated by reference herein intheir entirety.

The present invention is explained in greater detail in the non-limitingExamples set forth below.

EXAMPLE 1 Example Apparatus

A first embodiment of an apparatus (FIG. 2) of the invention was builtaround a “Rep-Rap” frame 16, which provides single-axis motion of thebuild platform 15, and up-down motion for the light source 11, belt 13,and a roller assembly 12 on which a belt is mounted. The belt wascreated from a TEFLON® fluorinated ethylene propylene film, CS Hyde ItemNo. 23-3FEP-24 (CS Hyde Co., 1351 N. Milwaukee Ave., Lake Villa, Ill.60046 USA). The roller assembly included a set of stepper motors androllers which cause the belt to roll along the assembly. A WINTECHPRO4500 ultraviolet digital light projector (available from WintechDigital Systems Technology Corp., 2888 Loker Ave. East, STE210C,Carlsbad, Calif. 92010 USA), was mounted onto the assembly, projectingan image onto the belt window formed by the orientation of the belt andthe roller assembly. In this embodiment, resin is applied to the partmanually before rolling the film over the part and exposing each layer;however, this can be automated with addition of an applicator such as aroller, sprayer (e.g., ink-jet spray head), blade, bath, or combinationthereof, or other suitable applicator, as described earlier, anddiscussed further below.

EXAMPLE 2 Fabrication of Three-Dimensional Objects

A UV-curable resin comprised of 76 parts Sartomer CN2920, 5 partsisobornyl acrylate, 19 parts cyclohexanedimethanol divinyl ether, 0.5parts Irgacure 819 photoinitiator, 0.04 parts Wikoff SCUV 14607 Black,and 0.16 parts Wikoff SCUV 14611 White was provided.

A test fabrication was performed using the resin was carried out withthe apparatus of Example 1, with a slice height of 100 microns andmanual application of the resin to the film on each pass. Results areshown in FIG. 3. Not including manual resin application (which will beautomated in future revisions and add minimal time), each layer tookapproximately 1.5 seconds (.5 second exposure, 1 second move). With aslice height of 100 microns, this correlates to a fabrication speed ofapproximately 240 millimeters per hour.

EXAMPLE 3 Mounting of Head Assembly to CNC Machine as Second DriveAssembly

A “head assembly” apparatus comprising a source of actinic radiation,belt to which polymerizable liquid is applied, applicator for applyingthe polymerizable liquid to the belt, and associated interconnectingframe, as described above, is mounted or retrofitted to a commercialvertical or horizontal CNC machine (which then serves as the seconddrive assembly) to provide high accuracy, long distance, travel invarious axes over a working bed or carrier for the object. Examples ofsuitable CNC machines include, but are not limited to, the HAAS VF-2,VF-4, and VF-12/40 vertical CNC machines, and the HAAS EC-400 and EC-400horizontal CNC machines, available from Haas Automation, Inc., 2800Sturgis Rd., Oxnard, Calif., 93030 USA.

EXAMPLE 4 Single and Multi-Pass Travel Paths

In the example above, the head assembly spanned the entire depth of thebuild platform, and can deposit an entire slice in one pass across theplatform (see FIG. 4). This will be referred to as single-passdeposition. Although this method provides excellent print speeds, it maybecome infeasible for very large build areas, or where veryhigh-resolution projectors are used (as the number of projectorsrequired would be high). In these situations, it may be desirable toswitch to multi-pass printing, where the projector assembly is narrower,no longer spanning the entire build platform, and instead requiresmultiple passes across the build platform at different lateral positionsto cover the entire build area. Of course, when printing cross-sectionsthat do not span the entire build platform, fewer passes may be neededto cover the entire cross-section.

EXAMPLE 5 Apparatus and Method with Co-Fabrication of Leading andTrailing Bumpers

An alternate embodiment of the invention, shown with a continuous belt13, and as operating in both directions, is given in FIGS. 5-6, withFIGS. 6-7 representing two successive passes in opposite directions. Apair of rollers 12 serves as the drive assembly and carries the belt,which passes along leading edge 28 and trailing edge 29 defining acontact zone therebetween, a portion of which is positioned beneath alight source 11 which then defines a curing zone 31. The belt is made ofan oxygen-permeable fluoropolymer. An LCD light panel 41, positionedadjacent the belt and having an associated ultraviolet light panel orsource, serves as the patterned light source, yet space is provided forthe back side of the belt to contact the atmosphere and allowatmospheric oxygen to pass therethrough. Polymerizable liquid is appliedto the belt by one or the other of two sets of spray applicators 22(e.g., ink jet cartridges), depending on the direction of travel. A pairof bumpers 47 are being produced, both incorporating ramps 48, and bothoptionally but preferably made from a different material than the object(applied to the belt in a spatially controlled manner from differentorifices in the applicator assembly). Motion of the “head assembly” (theapplicators, drive assembly, light source, and belt) relative to theobject and carrier is illustrated by the open arrow within the belt inboth Figures; corresponding motion of the carrier and object, relativeto the head assembly, is shown by the other open arrow within theobject. Dashed arrows show direction of travel of the belt. Vectors arematched so that, where the belt is in contact with the object, it issubstantially motionless or static—that is, there is no slippage of thebelt on the object. As the belt passes over the object, in eitherdirection, there is preferably left behind an “active surface” 32 or“gradient of polymerization” (e.g., due to residual inhibitor therein),to which active surface the newly deposited polymerizable liquid maycovalently bind. First and second drive assemblies are not shown, butnote that these two may be consolidated together as an XYZ drive, orsome may be existing drive components of a CNC machine, to which a “headassembly” comprised of the applicators, belt, light source, optionallyadditional drive components or at least rollers, all on a correspondingmounting frame, may be mounted or retrofitted.

EXAMPLE 6 Offset Curing Zones in Successive Deposition Passes

As will be appreciated by the foregoing, each of the repetition of thedeposition process increases the thickness of the growing object,pass-by-pass over the carrier and object. As schematically illustratedin FIG. 7, for each deposition pass the irradiation step may be carriedout as a series of separate successive exposures, with differentcross-hatching in each pass indicating successive separate exposureszones and curing zones. On subsequent passes or repeats, as the objectis grown in thickness, the exposure zones in the current pass may bealigned with the exposure zones in the immediate previous pass. Or, insome embodiments, the exposure zones in subsequent passes may bestaggered or offset (regularly or irregularly) from the exposure zonesin the immediate previous pass. Staggering may be accomplished by anysuitable means, including changing the width of one or more exposurezones at the beginning, end, or in-between portions of each pass (andcombinations thereof).

The foregoing is illustrative of the present invention, and is not to beconstrued as limiting thereof. The invention is defined by the followingclaims, with equivalents of the claims to be included therein.

That which is claimed is:
 1. A method of making a three-dimensionalobject, comprising: (a) providing an apparatus comprising a radiationsource, a carrier on which said three dimensional object is made, and amovable belt positioned therebetween, said belt having a first surfaceand an opposite second surface, with said belt comprised of an opticallytransparent material, and with said belt permeable to a polymerizationinhibitor; (b) applying a polymerizable liquid to said first surface ofsaid belt, and contacting said second surface of said belt to saidpolymerization inhibitor, (c) contacting a portion of said belt firstsurface having said polymerizable liquid thereon to said carrier or saidthree dimensional object so that said belt adheres thereto with saidpolymerizable liquid positioned therebetween; (d) irradiating saidpolymerizable liquid with actinic radiation through said belt from saidradiation source to polymerize the polymerizable liquid positionedtherebetween, and/or while: (i) moving said radiation source lengthwiseacross said substrate or said three-dimensional object; (ii)continuously adhering a leading edge portion of said belt to saidcarrier or said object; (iii) continuously peeling a trailing edgeportion of said belt from said carrier or said object, with (iv) saidpolymerization inhibitor passing through said belt to form an activesurface on said object, and optionally, a dead zone of unpolymerizedliquid between said active surface and said polymerizable liquid; then(e) optionally separating said belt from said carrier or said threedimensional object; and then (f) repeating steps (b) through (e) untilsaid three dimensional object is completed.
 2. The method of claim 1,wherein: said moving belt is configured to pass through a contact regionwhich contact region is in fixed contact with said carrier or saidobject, and said contact region has a length dimension less than that ofsaid carrier or said object.
 3. The method of claim 1, wherein saidirradiating step is carried out with patterned actinic radiation.
 4. Themethod of claim 1, wherein said applying step is carried out bypatterned coating of said belt with said polymerizable liquid.
 5. Themethod of claim 1, wherein said apparatus further comprises a frame,with said belt and said radiation source connected to said frame, andwith said contact region defined by said frame.
 6. The method of claim1, wherein said belt is continuous.
 7. The method of claim 1, whereinsaid belt is reversible in direction of travel.
 8. The method of claim1, wherein said separating step (e) is carried out by (i) advancing saidbelt contact region lengthwise beyond said carrier or said threedimensional object, and then (ii) advancing said belt contact region andsaid carrier or said three dimensional object in the height dimension.9. The method of claim 1, wherein said repeating step (f) is carried outby repeatedly reversing the direction of travel of said belt andradiation source.
 10. The method of claim 1, wherein said repeating step(f) is carried out by (i) spacing said belt above said three dimensionalobject; (ii) moving said belt and radiation source lengthwise acrosssaid three dimensional object without contacting the same to return saidbelt and radiation source to a start position; and (iii) repeating steps(b) through (e) in the same direction of travel as in the previousrepetition of steps (b) through (e)
 11. The method of claim 1, whereinsaid repeating step (f) further comprises laterally shifting said beltand radiation source with respect to said direction of travel prior torepeating steps (b) through (e).
 12. The method of claim 1, wherein saidbelt is electrostatically charged, and/or said applying step is carriedout by electrospray.
 13. The method of claim 1, further comprisingpressing said belt against said carrier or said object to promoteuniform coating of the object with the polymerizable liquid.
 14. Themethod of claim 1, wherein said polymerizable liquid has a viscosity atsaid contacting step of at least 1,000 centipoise.
 15. The method ofclaim 1, further comprising co-fabricating a sacrificial leading bumperand/or sacrificial trailing bumper with said object.
 16. The method ofclaim 1, wherein said belt is comprised of a fluoropolymer.
 17. Themethod of claim 1, wherein said radiation source comprises a lightsource.
 18. The method of claim 1, wherein: said polymerizable liquidcomprises a free radical polymerizable liquid and said inhibitorcomprises oxygen; or said first polymerizable liquid comprises anacid-catalyzed or cationically polymerizable liquid, and said inhibitorcomprises a base.
 19. The method of claim 1, wherein said irradiatingstep is carried out as a series of separate successive exposures thatoccur prior to each repeating step repeating step (f).
 20. The method ofclaim 19, wherein a subsequent series of successive exposures is offsetfrom an immediately prior series of successive exposures after at leastone, or a plurality of, said repeating steps (f).
 21. An apparatususeful for making a three-dimensional object, comprising: (a) aradiation source; (b) a carrier on which said three dimensional objectis made; (c) a movable belt positioned between said carrier and saidradiation source, said belt having a first surface and an oppositesecond surface, with said belt comprised of an optically transparentmaterial, and with said belt permeable to a polymerization inhibitor;(d) an applicator assembly operably associated with said belt andconfigured to apply a polymerizable liquid thereto; and (e) a frame,with said belt and said radiation source connected to said frame, andwith said frame defining a contact region in which said belt contactssaid carrier or object; (f) a first drive assembly interconnecting saidmovable belt and said frame; and (g) a second drive assemblyinterconnecting said frame and said carrier.
 22. The apparatus of claim21, wherein said applicator assembly comprises a roller, sprayer, blade,bath, or combination thereof.
 23. The apparatus of claim 21, whereinsaid applicator assembly comprises a plurality of independentlycontrollable spray orifices.
 24. The apparatus of claim 21, wherein saidradiation source comprises a light source.
 25. The apparatus of claim21, wherein said belt comprises a fluoropolymer.